Implantable cardioverter-defibrillators (ICDs) are used to provide various types of therapy to a cardiac patient, including, for example cardioversion and/or defibrillation. These devices consist of a hermetic housing implanted into a patient and connected to one or electrodes, combinations of which can define low-voltage therapy (pacing) vectors, high-voltage therapy (defibrillation) vectors, and/or sensing vectors. The housing of the ICD contains electronic circuitry for monitoring the condition of the patient's heart, usually through sensing electrodes, and also contains a battery, high voltage circuitry and control circuitry to generate, control and deliver the defibrillation shocks. Typically, one or more leads are connected to circuitry within the ICD and to one or more defibrillator electrodes proximate the heart. One example of an ICD is disclosed in U.S. Pat. No. 5,405,363 to Kroll et al., the disclosure of which is hereby incorporated by reference.
Dislodgement of a right ventricular (RV) transvenous defibrillation lead, for example, is a rare complication of ICD therapy. However, such dislodgement deserves attention out of proportion to its low incidence because lead dislodgement may cause fatal proarrhythmia if the lead enters the right atrium, even in a patient having a normal, physiological, sinus rhythm. For example, a patient having an ICD may exercise and increase the heart rate to 120 beats-per-minute (bpm) corresponding to an R-R interval of 500 ms and a P-R interval of 200 ms. Both the P-waves and the R-waves are sensed with alternating P-R and R-P intervals of 200 ms (equivalent to 300 bpm) and 300 ms (equivalent to 200 bpm), resulting in erroneous detection of ventricular fibrillation (VF) by the ICD.
In response to such an erroneous detection of VF, a shock synchronized to the atrial electrogram (EGM) will likely be delivered by the ICD during the ventricular vulnerable period, 300 ms after the preceding R-wave. In a typical case, the vector of this shock is from the defibrillation electrode coil on the right ventricular (RV) lead to the housing or can of the ICD. But because the RV lead has dislodged, the defibrillation electrode coil of the RV lead is now likely positioned within the right atrium. This vector is sufficient for cardioversion of atrial fibrillation, but not for ventricular defibrillation. Thus, the shock will likely be below both the ventricular upper limit of vulnerability, and the defibrillation threshold for this shock vector. Because of this, the shock has a high likelihood of inducing VF that the ICD cannot either sense or defibrillate due to the dislodgement of the RV lead.
In another circumstance, dislodgement of a transvenous ICD lead into the atrium may cause fatal proarrhythmia in a patient experiencing atrial fibrillation (AF). For example, the high rate of an AF can sometimes be falsely classified by the ICD as VF. In response, a shock synchronized to the atrial electrogram will likely be delivered by the ICD during the ventricular vulnerable period. The vector of this shock is from the coil on the RV lead to the housing or can of the ICD. But because the RV lead has dislodged, the coil of the RV lead is now likely positioned within the right atrium. Because the shock vector is inefficient (right atrium to ICD housing or “can”), the shock's strength will likely be below both the ventricular upper limit of vulnerability and the ventricular defibrillation threshold. Thus, the shock has a high likelihood of inducing VF that the ICD cannot defibrillate. A related risk in this situation may occur if the inappropriate shock from the dislodged RV lead successfully defibrillates (cardioverts) the atrium. If the ICD then senses only the atrial signals of normal rhythm from its ventricular sensing electrode on the dislodged RV lead, the ICD will classify the shock as successful and, despite the potential for a related or separate VF occurring, the ICD would not deliver another shock. The result will then be a fatal, untreated VF.
Lead dislodgement to the atrium presents a significant risk even if no inappropriate shock is delivered because the ICD is unlikely to defibrillate spontaneous VF with a shock vector based on the dislodged lead. Further, lead dislodgement within the ventricle presents a serious complication even if the lead does not reach the atrium: A transvenous lead with the tip dislodged and free to move about within the RV cavity may induce ventricular tachycardia or VF by mechanical trauma. Additionally, such a dislodged lead does not provide reliable ventricular sensing, bradycardia pacing, or antitachycardia pacing.
Presently, no ICD has implemented any proposed method or algorithm to consistently and effectively detect or mitigate lead electrode dislodgement. U.S. Pat. No. 9,572,990 to Gunderson (“the '990 Patent”), teaches an algorithm that withholds therapy in sinus rhythm based on an anticipated pattern of electrical signals on the ventricular near-field (NF) electrogram. As used in ICDs, the near-field electrogram ventricular is recorded from two closely-spaced electrodes near the tip of the lead, at least one of which is a small sensing electrode at the tip of the lead. Because these electrodes are closely spaced, their electrical “field of view” is short-range and dominated by the electrical signals originating in myocardium adjacent to the lead tip. The near-field electrogram is thus ideal for sensing local myocardial electrical activity, and all ICDs monitor the near-field electrogram continuously for the purpose of sensing the cardiac rhythm.
The '990 Patent teaches detection of lead dislodgement to the atrium by the recording of short-long-short-long (S-L-S-L) sequences of intervals between near-field electrogram signals. The “short” interval corresponds to the P-R interval; the “long” corresponds to the R-P interval. Additionally, the algorithm requires that each signal have a relatively low amplitude (e.g., 0.5-2.5 mV) and that a zero crossing occurs in the short interval to exclude R-wave double-counting. This algorithm alerts when two such sequences occur. Unfortunately, the sensitivity of this pattern for lead dislodgement to the atrium is unknown, and this algorithm cannot detect lead dislodgement until the lead tip enters the atrium.
Additionally, the algorithm described in the '990 Patent is not effective under a number of lead dislodgement to the atrium conditions that do not result in S-L-S-L sequences on the near-field electrogram. One example occurs when the atrial rhythm is AF so there are multiple atrial EGMs for each ventricular EGM. Other examples relate to the limited “field of view” near-field electrogram. Because this field of view is restricted to local myocardial electrical signals, it does not reliably record signals from two cardiac chambers (atrium and ventricle) simultaneously during the unpredictable conditions of lead dislodgement to the atrium. Further, the method of the '990 Patent cannot detect lead dislodgements in which the lead tip remains in the ventricle and does not reach the tricuspid valve because in this case, the near-field electrogram records a ventricular signal but no atrial signal.
In contrast to a near-field electrogram, a far-field electrogram is an EGM recorded by one or more electrodes located at a distance from the source of the EGM. A ventricular far-field electrogram records ventricular activation using at least one electrode that is not in a ventricle. As used in ICDs, the ventricular far-field electrogram usually refers to an EGM recorded between two or more large, widely-spaced electrodes, used to deliver defibrillation shocks, at least two of which have opposite polarity during the shock and are thus separated in space by a distance of 10 cm or more.
U.S. Patent Pub. No. 2016/0375239 to Swerdlow (“the '239 Application”), the disclosure of which is incorporated by reference herein, proposes, inter alia, diagnosing lead dislodgement using measurements made on the far-field electrogram including absolute amplitude changes and occurrence of the S-L-S-L pattern. This overcomes some limitations of the '990 Patent, for diagnosis of lead dislodgement to the atrium.
Methods are known in the art for the diagnosis of dislodgements of leads other than RV leads. For example, U.S. Pat. No. 5,713,932 to Gillberg et al. discloses a method of diagnosing atrial lead dislodgement to the ventricle limited to patients who have intact atrioventricular conduction. Atrial lead dislodgement to the ventricle is diagnosed if the atrial lead is paced and the interval from the atrial pacing pulse to the ventricular near-field electrogram is less than the expected delay from atrioventricular conduction. U.S. Pat. No. 7,664,550 to Eik et al. discloses a method for diagnosing dislodgement of left-ventricular lead placed within a venous branch of the coronary sinus. This method involves difference in waveforms related to larger atrial and smaller ventricular signals when the lead dislodges. Similarly, U.S. Pat. No. 9,327,131 to Ryu et al. discloses a method for diagnosing dislodgement focused on left-ventricular leads based on the relative amplitude of atrial and ventricular signals.
A need remains, therefore, for improved methods and systems of detecting lead electrode dislodgement.